Upflow anaerobic sludge blanket (UASB) reactor was installed to replace the conventional anaerobic lagoon treating bagasse wash wastewater from agro-based pulp and paper mill, to generate bio-energy and to reduce greenhouse gas emissions. The plant was designed to treat 12 ML d(-1) of wastewater having two 5 ML capacity reactors, 5.75 kg COD m(-3) d(-1) organic loading rate and 20h hydraulic retention time. In the plant 80-85% COD reduction was achieved with biogas production factor of 520 L kg(-1) COD reduced. In 11 months 4.4 million in 3 of biogas was generated from bagasse wash wastewater utilizing UASB process. Utilization of the biogas in the Lime Kiln saved 2.14 ML of furnace oil in 9 months. Besides significant economic benefits, furnace oil saving reduced 6.4 Gg CO2 emission from fossil fuel and conversion of the anaerobic lagoon into anaerobic reactor reduced 2.1 Gg methane emission which is equal to 43.8 Gg of CO2. (c) 2005 Elsevier Ltd. All rights reserved.